In recent years, significant attention has been paid to magnetic particles, and iron particles in particular, which are commonly used because of their excellent magnetic properties. They can be applied in various fields of technologies, in biomedical applications, absorption and catalyst processes or to produce magnetorheological fluids and composites. Depending on desired dimensions, the iron particles can be nano-, micro- or macroscopic in size.
Carbonyl iron particles, for example, are primary components for the design of magnetic type electromagnetic wave absorbers. Carbonyl iron is substantially pure iron (99.9% iron content or greater) formed from iron containing carbonyl moieties (e.g., Fe(CO)5). Carbonyl iron powder (CIP), for example, has specific magnetic properties useful for many applications and would be a desirable additive for a coating due to these magnetic properties. However, carbonyl iron is susceptibile to oxidation and corrosion at high temperatures leading to a decrease in magnetic properties. Furthermore, uniform dispersion of CIP is a challenge and failure to have proper dispersion can impact CIP performance. For example, methods, such as coating the particle with a polymer, can cause agglomeration of the particles and dispersion of the particles can be hindered.
Silica iron, for example, has been used instead of carbonyl iron because it is less susceptible to corrosion and easier to process. Known passivation techniques for carbonyl iron or silica iron include: carbon dioxide passivation, electroless plating of cobalt, polyaniline passivation, microwave plasma processes, as well as silica coatings. These processes involve numerous/complex processing steps, result in substantial increases in the mass and volume of the particle, cause agglomeration of the resulting particles, and can diminish the particles' magnetic properties.
There is a need for passivated iron particles with retained or improved magnetic properties and improved methods for passivating iron particles.